Condensation & Rarefaction of Air. 521

EXPERIMENT 7.

On condensed Air.

Took a large spherical glass receiver,the capa-city of which was something more than twicethat of the former (above one gallon), and sus-pended a thermometer in the centre of it, of alarger bulb than that before used ; the receiverhad a brass cap and stop-cock adapted to it:Then doubled the density of the air within itby a condenser. The thermometer rose 2° or- more. Let out the air suddenly and the ther-mometer immediately sunk each time from 3 0to 3 0 . 5 ; at the same time an exceedingly densemist was produced in the receiver, which soonsubsided.

Suspecting that aqueous vapour, which alwaysexists in the atmosphere, and is liable to assumethe liquid or aerial form according to circum-stances, might be the principal agent in the pro-duction of heat and cold by condensation andrarefaction, I thought that an increase of it mightproduce a greater effect, and that cold air, whichcontains less vapour, might have a less effect.The reverse however was the fact, as appears bythe following,